A wide variety of transfer mechanisms are known for establishing a connection across a network. Thus a connection may involve the establishment of a physical circuit through the network, in which case data to be transferred need not be divided up into units or if it is need carry no routing or connection indicator. Alternatively, a connection may involve transferring data in data units which are individually routed along the same or different network paths (such as with TCP packets on the Internet) in which case the data units carry information about their eventual destination. Again, a connection may involve the establishment of a virtual circuit (such as in ATM) in which case the individual data units need only carry information about their next hop, the network nodes being responsible for routing and updating the units as required.
Whatever the transfer mechanism employed for a connection, a network operator such as a national PTT offers services to users on the basis of a user "purchasing" a connection across the network. The amount paid for the connection will depend on characteristics of the connection such as its bandwidth and reliability; such parameters may be generally be considered as measures of the quality of service provided by the connection. Of course, whilst the network operator may offer to provide connections with a particular quality of service, this is no guarentee that the connections actually established do indeed provide this quality of service.
Whilst the actual quality of service provided by a connection has always been a concern for a user purchasing a connection from a network operator, the coming of broadband networks has substantially increased interest in this area because of the complexities involved in defining the exact quality of service contracted for. Quality of service in this context includes agreed bandwidth and the network operator must manage the available bandwidth so that, on average, all client contracts can be met. More particularly, for broadband connections, quality of service measurements may include:
unit delay . . . the amount by which a unit has been delayed or the average by which some sequence of units has been delayed; PA1 delay variation . . . the amount by which the unit delay varies; PA1 unit loss . . . the proportion of units that entered the network but never left it; PA1 unit corruption . . . the proportion of units that entered the network and left it, but whose contents had been corrupted; PA1 burst dispersion . . . the extent to which passage through the network has changed the spacing between units, usually by delaying the end of a burst by more than the start; PA1 peak bandwidth . . . the maximum bandwidth delivered at the network exit point; PA1 mean bandwidth . . . the mean bandwidth delivered at the network exit point; PA1 low bandwidth . . . the minimum bandwidth delivered at the network exit point; PA1 respective event-capture means at each of said first and second points, each event-capture means comprising: PA1 correlation means for receiving the source and sink report streams and for pairing from the two streams those event reports that relate to the same the event by matching their signatures, the event reports so paired constituting matched event-report pairs; and PA1 measurement means for utilising the matched event-report pairs to derive quality of service measurements therefrom in respect of the operation of the connection between said first and second points. PA1 a criterion based on the absolute value of a time stamp associated with a data unit, PA1 a criterion based on the relative time of receipt of at least two data units as indicated by their associated time stamps. PA1 (a) monitoring the network at each said point to identify data units associated with the connection of interest; PA1 (b) determining at each said point whether data units identified in step (a) at that point satisfy a predetermined criterion set of one or more criteria applicable to a group of at least one data unit associated with the connection of interest, the criterion sets for the first and second points being non mutualy exclusive and the satisfaction of the criterion set constituting an event; PA1 (c) generating for each said event determined in (b) an event report having a signature characterisitic of that specific event, the signatures being derived from the data units associated with the corresponding events and the event reports generated for events at said first and second points respectively forming a source report stream and a sink report stream; PA1 (d) correlating the source and sink report streams to pair those event reports that relate to the same event by matching their signatures, the event reports so paired constituting matched event-report pairs; and PA1 (e) utilising the matched event-report pairs to derive quality of service measurements therefrom in respect of the operation of the connection of interest between said first and second points.
The last three measures may be viewed as profiling information as they can be derived for measurements at one point (the network exit point).
It is known to make quality of service measurements on a connection by injecting special test data units at a first network point and then detecting these special test data units at a second network point. However, such an approach suffers from the drawback that the test data units will inevitably have an influence on the parameters being measured, this being particularly true if the number of test data units injected is significant. It is also difficult to intersperse the test data units with the normal traffic in a consistent manner. Furthermore, it is necessary to remove the test data units prior to them reaching the intended destination end point of the connection and this requires the use of an active probe which is both more expensive and carries higher risks for operational integrity than a passive probe.
It is an object of the invention to provide a method and apparatus for carrying out quality of service measurements on a connection across a network, that do not suffer from the above-mentioned drawbacks.